When designing contemporary vehicles, automotive designers are faced with many compromises. One such compromise is weight of automotive components versus their mechanical strength versus their cost of production. In order to try to improve this particular compromise, ultralight steel automotive parts have recently been manufactured by employing hydroforming manufacturing processes. Simply stated, hydroforming employs water or hydraulic fluids at high pressure to provide forces for shaping a given component part. Hydroformed components can be generated either by forming metal sheet or metal tubing.
Hydroforming of tubing is often employed when a complex automotive shape is required. For example, in a hydroforming process, a bent section of seam-welded cold-rolled steel tubing is placed in a closed die set, and then a pressurized fluid is introduced into ends of the tube, reshaping the tube to a confine of a cavity provided by the closed die set.
Hydroforming of sheet steel is contemporarily implemented by two methods. In a first method, a steel sheet is deformed into a female cavity by water under pressure from a pump or by press action to generate a hydroformed component. In a second such method, a steel sheet is deformed by a male punch, which acts against a fluid under pressure. Sheet hydroforming provides a work-hardening effect as the steel sheet is forced against die surfaces by action of fluid pressure. Hydroforming provides aforementioned automotive designers with an opportunity to employ lighter thinner-gauge steels while maintaining component performance.
It is known to fabricate side roof rails, front fender supports and pass-through members of automotive bodies by employing hydroforming processes. For example, in a published international patent application no. PCT/CA98/00962 (WO 99/20516), there is described a hydroformed space frame for a motor vehicle. The space frame is described as comprising first and second hydroformed longitudinally-extending tubular lower side rails. The lower said rails are laterally spaced from one another and are disposed in a generally parallel relation to one another. Moreover, the space frame is further described to include a pair of generally parallel hydroformed tubular upper longitudinal structures, each structure being an integrally-formed structure fixed to an associated one of the lower side rails. Each upper longitudinal structure has a longitudinally-extending portion constructed and arranged to support a roof of the motor vehicle, each longitudinally-extending portion extending longitudinally between an upper end of an A-pillar of the space frame and an upper end of a rearward-most pillar of the space frame. Laterally extending connecting structural connects are disclosed for connecting the lower side rails to one another. Thus, it is known to employ hydroformed components for, in operation, substantially horizontal structural components of space frames for vehicles.
The aforementioned international PCT application concerns a vehicle including a roof structure. In road vehicles devoid of a strengthening roof structure, for example in open-top road vehicles such as cabriolets and soft-top sports vehicles, it is not possible for associated automotive designers to rely on roof structures to provide vehicle occupant protection which represents a technical problem. Conventionally, it has been accepted that such open-top vehicles are potentially not as protected in crash or impact situations in comparison to vehicles including strengthening roof structures. Moreover, it has been appreciated by designers that remaining support pillars and members employed in manufacturing open-top vehicles need to be relatively stronger to provide at least an acceptable degree of protection for vehicle occupants; such strength not only concerns the support pillars themselves but also a manner in which they are incorporated into corresponding vehicles.